Development and adaptation of dynamic models for new power generation source

Abstract

This dissertation’s main aim was to adapt a generic gas turbine and combined cycle power plant dynamic model for use in the power system simulation software, DigSilent PowerFactory. Due to the advantages in overall efficiency and lower emissions compared to conventional coal fired power plants, combined cycle power plants have gained popularity. Combined cycle power plants have become a significant portion in power generation across the world in recent times. Due to changes in the world to minimise carbon-dioxide footprints, there is demand for cleaner methods of power generation. In South Africa, the main power source is still coal fired power stations, but in recent times, gas turbine power plants were added to the power system. Approximately two-thirds of the generation capacity in a combined cycle power plant is produced by the gas turbines. The other third is generated by the steam turbine. Using the steam that is available means the overall efficiency of the power plant is improved and the emissions are decreased. Gas turbines and their controls are significantly different from the controls of a conventional steam turbine plant. In particular, the maximum output power of the gas turbine is very dependent on the deviation of its operating frequency from the rated frequency (or speed of the gas turbine), and the ambient conditions in which the gas turbine operates. In an effort to provide the industry with a single document and simulation model that summarises the unique characteristics, controls and protection of combined cycle power plants, the Cigre Task Force 25 was formed [1]. The aim of this Task Force was to develop an open cycle gas turbine (a more detailed model than existing models) and a combined cycle power plant simulation model, as no detailed models existed in any power system simulation software. The aim of this dissertation was to adapt the Cigre simulation models, enabling their use in the DigSilent PowerFactory power system simulation software and validate their performance.